The proposed research is divided into two parts, each of which involves application of NMR spectroscopy to problems in conformational analysis or structural determination. In part I, hindered rotation and nitrogen inversion in acyl aziridines will be studied by dynamic NMR spectroscopy to obtain information about the importance of conjugation in the amide bond of these compounds, and to demonstrate that pyramidal nitrogen in a amide can still PI-bond effectively with the carbonyl group. In part II, the usefulness of 170 NMR in dynamic NMR will be examined (e.g., N-tertbutyl nitramine and o-nitroaniline), and 170 spectra of the carbonyl oxygens in R-COX (X = SR, SeR) will be taken to provide information about the PI-donating abilities of X. The ability of 33S NMR to distinguish between singly and doubly bonded sulfur will be determined, and the beta and gamma effects will be measured for a series of mercaptans and sulfides. Solvents near the critical temperature will be used in some cases to reduce line widths. Many compounds of biological importance contain oxygen or sulfur, and the spectra will provide information about the potential of 170 or 33S NMR for studies of these compounds.